Selective serotonin reuptake inhibitors (hereinafter referred to as SSRIs) have become first choice therapeutics in the treatment of depression, certain forms of anxiety and social phobias, because they are effective, well tolerated and have a favourable safety profile compared to the classic tricyclic antidepressants.
However, clinical studies on depression indicate that non-response to SSRIs is substantial, up to 30%. Another, often neglected, factor in antidepressant treatment is compliance, which has a rather profound effect on the patient's motivation to continue pharmacotherapy.
First of all, there is the delay in therapeutic effect of SSRIs. Sometimes symptoms even worsen during the first weeks of treatment. Secondly, sexual dysfunction is a side effect common to all SSRIs. Without addressing these problems, real progress in the pharmacotherapy of depression and anxiety disorders is not likely to happen.
In order to cope with non-response, psychiatrists sometimes make use of augmentation strategies. Augmentation of antidepressant therapy may be accomplished through the co-administration of mood stabilizers such as lithium carbonate or triiodothyronin or by the use of electroshock.
The effect of combined administration of a compound that inhibits serotonin reuptake and a 5-HT1A receptor antagonist has been evaluated in several studies (Innis et al. Eur. J. Pharmacol. 1987, 143, 1095–204 and Gartside Br. J. Pharmacol. 1995, 115, 1064–1070, Blier et al. Trends in Pharmacol. Science 1994, 15, 220). In these studies, it was found that 5-HT1A receptor antagonists would abolish the initial brake on 5-HT neurotransmission induced by the serotonin reuptake inhibitors and thus produce an immediate boost of 5-HT transmission and a rapid onset of therapeutic action.
Several patent applications have been filed, which cover the use of a combination of a 5-HT1A antagonist and a serotonin reuptake inhibitor for the treatment of depression (see e.g. EP-A2-687472 and EP-A2-714663).
Another approach to increase terminal 5-HT would be through blockade of the 5-HT1B autoreceptor. Microdialysis experiments in rats have indeed shown that increase of hippocampal 5-HT by citalopram is potentiated by GMC 2-29, an experimental 5-HT1B receptor antagonist.
Several patent applications covering the combination of an SSRI and a 5-HT1B antagonist or partial agonist have also been filed (WO 97/28141, WO 96/03400, EP-A-701819 and WO 99/13877).
It has previously been found that the combination of a serotonin reuptake inhibitor with a compound having 5-HT2C antagonistic or inverse agonistic effect (compounds having a negative efficacy at the 5-HT2C receptor) provides a considerable increase in the level of 5-HT in terminal areas, as measured in microdialysis experiments (WO 01/41701). This would imply a shorter onset of antidepressant effect in the clinic and an augmentation or potentiation of the therapeutic effect of the serotonin reuptake inhibitor (SRI).
The present invention provides compounds which are serotonin reuptake inhibitors for the treatment of affective disorders such as depression, anxiety disorders including general anxiety disorder and panic disorder and obsessive compulsive disorder. Some of the compounds also have a combined effect of serotonin reuptake inhibition and 5-HT2c receptor modulation, which according to WO01/41701 would imply a faster onset of anti-depressant activity.
A few of the compounds embraced by the present invention have previously been described in WO 01/49681 and in WO02/59108. However, the compounds of WO01/49681 are not disclosed as having any therapeutic or biological activity. The compounds of WO02/59108 are disclosed as intermediates in the synthesis of compounds different from the compounds of the present invention with a terapeutic activity as melanocortin receptor agonists. One compound, 1-(2-phenoxyphenyl)-piperazine, embraced by the present invention, is disclosed in U.S. Pat. No. 4,064,245 as being useful in the treatment of metabolic disorders.